## [1204.6242] The Electromagnetic Signals of Compact Binary Mergers

Authors: T. Piran, E. Nakar, S. Rosswog

Date: 27 Apr 2012

Abstract: Compact binary mergers are prime sources of gravitational waves (GWs), targeted by current and next generation detectors. The question "what is the observable electromagnetic (EM) signature of a compact binary merger?" is an intriguing one with crucial consequences to the quest for gravitational waves. We present a large set of numerical simulations that focus on the electromagnetic signals that emerge from the dynamically ejected sub-relativistic material. These outflows produce on a time scale of a day macronovae - short-lived optical/UV signals powered by radioactive decay. In addition, the outflow interaction with the surrounding matter inevitably leads to a long-lasting radio emission. We calculate the expected radio signals from these outflows on time scales longer than a year, when the sub-relativistic ejecta dominate the emission. We discuss their detectability in 1.4 GHz and 150 MHz and compare it with an updated estimate of the detectability of short GRBs' orphan afterglows. We find that mergers with characteristics similar to those of the Galactic neutron star binary population (similar masses and typical circum-merger Galactic disk density of $1 {\rm cmˆ{-3}}$) that take place at the detection horizon of advanced GW detectors (300 Mpc) yield 1.4 GHz [150 MHz] signals of $\sim 50$ [300] $\mu$Jy, for several years. The signal on time scales of weeks, is dominated by the mildly and/or ultra relativistic outflow, which is not accounted for by our simulations, and is expected to be even brighter. Upcoming all sky surveys are expected to detect a few dozen, and possibly more, merger remnants at any given time thereby providing robust merger rate estimates even before the advanced GW detectors become operational. The macronovae signals from the same distance peak in the optical/UV at an observed magnitude of 22-23 about 10 hours after the merger.

#### May 11, 2012

1204.6242 (/preprints)
2012-05-11, 18:36